Heat Transfer Characteristics of Turbulent Flow in a Square Channel With Angled Discrete Ribs

Abstract

Experiments have been conducted to study the turbulent heat transfer and friction for fully developed flow of air in a square channel in which two opposite walls are roughened with 90° full ribs, parallel and crossed full ribs with angles-of-attack (α) of 60° and 45°, 90° discrete ribs, and parallel and crossed discrete ribs with = 60°, 45°, and 30°. The discrete ribs are staggered in alternate rows of three and two ribs. Results are obtained for a rib height-to-channel hydraulic diameter ratio of 0.0625, a rib pitch-to-height ratio of 10, and Reynolds numbers between 10,000 and 80,000. Parallel angled discrete ribs are superior to 90° discrete ribs and parallel angled full ribs, and are recommended for internal cooling passages in gas turbine airfoils. For α = 60° and 45°, parallel discrete ribs have higher ribbed wall heat transfer, lower smooth wall heat transfer, and lower channel pressure drop than parallel full ribs. Parallel 60° discrete ribs have the highest ribbed wall heat transfer and parallel 30° discrete ribs cause the lowest pressure drop. The heat transfer and pressure drops in crossed angled full and discrete rib cases are all lower than those in the corresponding 90° and parallel angled rib cases. Crossed arrays of angled ribs have poor thermal performance and are not recommended.

Effects of Length and Configuration of Transverse Discrete Ribs on Heat Transfer and Friction for Turbulent Flow in a Square Channel

“…The open air flow loop is similar to that used in two earlier studies (Lau et aL, 1989(Lau et aL, , 1990. It consists of two centrifugal blowers connected in parallel (one blower for low flow rate tests), two gate valves, a calibrated orifice flow meter, a flow straightener, an entrance section, and the test section (see Fig.…”

“…It consists of two centrifugal blowers connected in parallel (one blower for low flow rate tests), two gate valves, a calibrated orifice flow meter, a flow straightener, an entrance section, and the test section (see Fig. The test section is the straight, aluminum square channel used in Lau et aL (1989Lau et aL ( , 1990 The interior surfaces of two opposite walls of the test channel are roughened with transverse full or discrete ribs (see Fig. The test section is the straight, aluminum square channel used in Lau et aL (1989Lau et aL ( , 1990 The interior surfaces of two opposite walls of the test channel are roughened with transverse full or discrete ribs (see Fig.…”

“…2). 1 and Table 1 Readers are referred to Lau et al (1989Lau et al ( ,1990 for detailed descriptions of the test apparatus, the instrumentations and the experimental procedure. 1 and Table 1 Readers are referred to Lau et al (1989Lau et al ( ,1990 for detailed descriptions of the test apparatus, the instrumentations and the experimental procedure.…”

“…Therefore, longer rib segments improve the ribbed wall heat transfer more than shorter rib segments.The interaction between flow separation at the ends of discrete ribs and flow separation (and subsequent reattachment downstream) from the top edges of the ribs was believed to cause the higher heat transfer to the airstream in the discrete rib cases(Lau et aL, 1989(Lau et aL, , 1990. For p/e = 20, the staggered lxl ribs (case 8) also have higher values of St r /St" than the staggered 2x1 ribs (case 9).…”

Heat/Mass Transfer Distribution in a Rotating Two‐Pass Square Channel Part I: Regional Heat Transfer, Smooth Channel

“…A significant amount of experimental data is available in the literature on heat and mass transfer and pressure drop for turbulent flows in stationary multipass channels with smooth walls or ribroughened walls, for instance, Burggraf [1970], Webb et al [1971], Donne and Meyer [1977], Han et al [1988,1991], Lau et al [1991aLau et al [ , 1991bLau et al [ , 1991c, and Kukreja et al [1993]. Metzger and Sahm [1986] and Fan and Metzger [1987] studied the effect of channel geometry on the heat transfer in smooth rectangular channels with a sharp 180 turn whose walls were maintained at a uniform temperature.…”